As an electronic part using a semiconductor silicon substrate, such a solar battery element as shown in FIG. 1 has been widely known. As is understood from FIG. 1, the solar battery element comprises a P-type semiconductor silicon substrate 1 having a thickness of about 200 μm, a N-type semiconductor silicon layer 2 formed on a light receiving surface of the substrate 1, an antireflective film 3 such as a silicon nitride film or the like formed on an outer surface of the light receiving surface for increasing a light receiving efficiency and surface electrodes 4 formed on the antireflective film 3 and connected to the semiconductors. On a back side of the P-type semiconductor silicon substrate 1, there is evenly formed an aluminum electrode layer 5.
Usually, for producing the aluminum electrode layer 5, an aluminum paste material consisting of aluminum powder, glass frit and organic vehicle that contains binder such as ethyl cellulose, acrylic resin or the like is applied to a given portion by a screen printing method, and thereafter, the applied aluminum paste material is subjected to a short time firing at a temperature of about 600 to 900° C.
Due to the firing of the aluminum paste, aluminum is diffused to the P-type semiconductor silicon substrate 1, and thus, a Si—Al eutectic layer called as BSF (viz., Back Surface Field) layer 6 is formed between the aluminum electrode layer 5 and the P-type semiconductor silicon substrate 1, and due to the diffusion of aluminum, an impurity layer P+ layer 7 is produced.
This P+ layer 7 functions to restrain the loss caused by rejoining of carriers produced by a photovoltaic effect of PN junction and contributes to increase the conversion efficiency of the solar battery element.
It has been disclosed (by for example Patent Documents 1 and 2) that a higher BSF effect can be obtained when glass having a lead contained therein is used as a glass frit contained in the aluminum paste.